as far as bunker goes, I'd mainly say it can be useful when you're fighting the chaos tower bosses. You'd just hit them with whatever skill so they go to attack you, activate bunker, then proceed with your skill rotation.
outside of ct though, it's not very good. You're stuck in place until the duration ends or the bunker is otherwise destroyed. Some of the later monsters like disgruntled davids still chew through it anyway. I don't have release yet, I'd imagine that'd make bunker somewhat more practical but I can't say for sure.